Silicone defoamers have been widely used in the steps associated with foaming such as in the fields of chemical industries, food industries, petroleum industries, paper-making industries, textile industries, and pharmaceutical industries. There have been versatilely employed oil compound-type defoamers wherein silicone oils such as dimethylpolysiloxane, methylphenylpolysiloxane, and methylvinylpolysiloxane and the like and finely divided silica are mixed together.
In practical applications, there have been proposed emulsion defoamers wherein such oil compounds are dispersed in water along with surfactants, and self-emulsifying defoamers using polyoxyalkylene group-modified organopolysiloxanes and oil compounds in combination JP-A S51-71886, JP-B S54-43015, JP-B S52-19836, JP-B S52-22638 and JP-B S55-23084. The defoaming performance of these defoamers owes much to the starting oil compound, and related-art counterparts have been short of the defoaming performance in some cases. For one instance, some problems have arisen including the shortage of initial defoaming performance, the lowering of defoaming performance with time ascribed to long-term contact with foaming liquids, which have become pronounced, especially with the case where a foaming liquid is alkaline in nature.
A variety of proposals have been made in order to overcome these problems and more improve the defoaming performance. For instance, mention is made of a method wherein silica used in an oil compound has been preliminarily hydrophobized such as with chlorosilane in JP-B S52-31836 and a method of treating silica with a nitrogen-containing organosilicon compound in JP-B S51-35556. Nevertheless, the resulting performance has never been satisfactory and particularly, the defoaming performance has lowered with time in some cases. Thus, there has been a demand of further improving the performance.
In order to cope with these problems, there have been recently proposed a self-emulsifying defoamer composition in Japanese Patent No. 4232031 and an emulsion defoamer composition in JP-A 2007-222812 wherein hydrophobic organopolysiloxanes and finely divided silica surface-treated with an organopolysiloxane are treated under mixing in the presence of an alkaline catalyst to enhance an alkali resistance.
These defoamer compositions have a high defoaming performance, and such an alkali resistance as to undergo less time degradation in alkaline foaming liquids can be obtained. Nevertheless, the defoaming performance may become short under such severe conditions that a foaming liquid used is very high in alkalinity, an amount of a surfactant contained in a foaming liquid is very large, and an agitation force in an employed step is very intense. Thus, a further improvement of the performance has been demanded. In addition, with known defoamer compositions, a quantitative evaluation method for confirming a defoaming performance has never been known. Hence, evaluation has to be made for confirming the performance under practically employed conditions or similar conditions thereof on a case-by-case basis.